It is known to use redundant circuits, in particular in radio frequency amplifier equipment.
Such a redundant circuit arrangement according to the genus-forming prior art, such as is known basically from U.S. Pat. No. 5,418,490, comprises an amplifier circuit which is provided between an input gate and an output gate. This amplifier circuit has two amplifier stages which are connected in parallel, both stages being capable of being switched on and off at the input end and the output end by using a switch, generally a relay switch. One of the two amplifier stages is connected through via the input-end and output-end relay, whereas the input and output of the second amplifier stage which is arranged in parallel is switched off. If the amplifier stage which is switched on fails, the contacts of the input-end and output-end relays are switched over to the second amplifier which was previously not required. If the second amplifier stage should also fail, in each case one relay switch is also connected in series with the input-end and output-end switchover relays in order to switch over between the two amplifier stages so that in such a case a through-connection path which is parallel with the two amplifier stages is connected through while bypassing both amplifiers.
Arrangements in which both parallel amplifier stages are connected together continuously in a parallel mode are basically also known. If one amplifier stage fails, at least the second amplifier stage remains active. However, a failure in an amplifier stage leads to a reduction in amplification (for example of 4 to 8 dB) and to an increase in the noise coefficient by, for example 2 to 4 dB. In addition, there is no optimum adaptation to the input and output. This operating state must therefore be referred to as a worsened operating condition which makes repair absolutely necessary. A further problem with this arrangement is that, for example, in the case of an electrical discharge (lightning strike, etc.) both amplifier stages may also fail in this case, as both amplifier stages are basically operating in parallel.
The technology herein provides an amplifier switch which is improved in comparison with the above, in particular for a circuit having at least two amplifier circuits or amplifier stages, in which case the amplifier switch is to have in particular a low throughput attenuation in the bypass mode and a very good adaptation in the amplifier mode.
The technology herein uses surprisingly simple means to achieve significant improvements in comparison with the prior art.
The amplifier switch according to an exemplary illustrative non-limiting arrangement herein can already be implemented with a single amplifier circuit or stage. Whereas, in the prior art, the switch, preferably in the form of a relay, has to be provided respectively both at the input end and at the output end for a switching over process so that, in the case of a defect, it is possible to switch over from the amplifier branch into a bridging path in parallel with the amplifier branch, according to an exemplary illustrative non-limiting implementation, only a single switch, i.e. generally a switch relay, is now arranged at the input or at the output. The bridging path which leads from a switching contact of the switch device to a summing point in the amplifier path is now dimensioned in such a way that the electrical length is approximately λ/2. In other words, the open relay contact is operated across the λ/2-long bridging line with high impedance, transformed to the opposite gate, i.e. in the open circuit mode.
According to one preferred exemplary illustrative non-limiting implementation, a PIN diode is also connected in the amplifier line between the amplifier and the summing point. This is because, if the amplifier stage is not operational, a connection without a PIN diode could lead to increased loading in the bridging line and throughput line. The amplifier stage can be connected with high impedance to the line by means of the PIN diode.
According to an exemplary illustrative non-limiting implementation, only one switch relay (in comparison with at least two switches in the prior art) is therefore necessary.
However, the advantages according to an exemplary illustrative non-limiting implementation are apparent, especially in the design of a redundant circuit.
This is because, in one particularly preferred exemplary non-limiting illustrative implementation, such a redundant circuit is then constructed with at least two amplifiers or amplifier stages in such a way that they are not connected in parallel with one another as in the prior art but rather cascaded in series. There are also no decoupling problems in this context.
The exemplary illustrative circuit operates here in such a way that in each case only one amplifier circuit and amplifier stage is switched on in a home position, when the respective bridging line is switched on by switching over the switch or relay, the amplifier there is thus switched off. If the activated amplifier stage fails, the relay can switch over to the bridging path, the relay or the switch of the further amplifier stage interrupting the connection to the bridging line and switching over in order to activate the associated amplifier stage. As a result, the same electrical conditions are always precisely present so that no damping problems or adaptation problems or other problems occur.
Above all, such a redundant circuit with two amplifier stages requires only two switches which may be arranged either on the input side or output side in relation to the respective amplifier stage.